Light emitting diode and fabrication method therof

ABSTRACT

A light-emitting diode includes from bottom to up: a substrate, a first-conductive type semiconductor layer, a super lattice, a multi-quantum well layer and a second-conductive type semiconductor layer. At least one layer of granular medium layer is inserted in the super lattice. The granular medium layer is used for forming V pits with different widths and depths in the super lattice. The multi-quantum well layer fills up the V pits and is over the top surface of the super lattice. The number of micro-particle generations, positions and densities can be adjusted by introducing granular medium layers and controlling the number of layers, position and growth conditions during super lattice growth process, to ensure V pits of different depths and densities. This can change hole injection effect, effectively improve hole injection efficiency and distribution uniformity in all quantum wells, thus improving LED light-emitting efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority to,PCT/CN2016/097803 filed on Sep. 1, 2016, which claims priority toChinese Patent Application No. 201510727669.5 filed on Nov. 2, 2015. Thedisclosures of these applications are hereby incorporated by referencein their entirety.

BACKGROUND

Light Emitting Diode (LED) is a semiconductor solid light-emittingdevice, using semiconductor PN junction as the light-emitting materialfor direct photovoltaic conversion. At present, the InGaN/GaNlight-emitting diode is regarded as the most potential light-emittingsource. However, due to low hole concentration and hole mobility of theP-GaN material, the injection depth in the multi-quantum well (MQW) islimited, which greatly restricts further improvement of GaN-based LEDlight-emitting efficiency.

SUMMARY

The inventors of the present disclosure have recognized that, asverified by more theoretical research and test results, V-type defectsare very important hole injection channels in the GaN-based LED, whichgreatly improves hole injection efficiency. The principle for V pitsnaturally formed in conventional structure is that: the super latticegrowth layer is of low temperature, and the nitride (such as GaN) haspoor lateral epitaxy. This time, V pits would be formed due to threadingdislocation. However, as TEM and AFM analysis shown, initial formationpositions and sizes of V pits are basically consistent. As a result,hole injection efficiency in specific multi-quantum well (QW) positionis high, yet injection efficiency in other quantum wells (QWs) is low,which influences lighting efficiency.

The present disclosure is to provide a LED epitaxial structure andfabrication method thereof, wherein, a granular medium layer is insertedto form V pits of different widths and depths, which greatly improveshole injection efficiency in the LED and the space distribution of holesin MQW, thus improving hole utilization efficiency of all QWs andlighting efficiency of LED.

According to one aspect of the present disclosure, a light-emittingdiode with high hole injection efficiency is provided, including frombottom to up: a substrate, a first-conductive type semiconductor layer,a super lattice, a multi-quantum well layer and a second-conductive typesemiconductor layer; wherein, at least one granular medium layer isembedded in the super lattice; wherein, the granular medium layer isused for forming V pits with different widths and depths in the superlattice; and the multi-quantum well layer fills up the V pits and isover the top surface of the super lattice.

In some embodiments, form a buffer layer over the substrate, whichprefers to be InAlGaN.

In some embodiments, the first-conductive type semiconductor layerincludes an N-GaN layer, or includes a U-GaN layer and an N-GaN layer.

In some embodiments, the second-conductive type semiconductor layerincludes a P-GaN layer, or includes an electronic blocking layer and aP-GaN layer, or includes an electronic blocking layer, a P-GaN layer anda contact layer.

In some embodiments, the grain size of the granular medium layer is0.5-5 nm, and the V pits are 50-500 nm wide.

In some embodiments, the depth H of the V pits depends on the totalthickness of the super lattice T1, the total thickness of themulti-quantum well layer T2 and the position of the granular mediumlayer in the super lattice layer, and satisfies T2<H<T1+T2.

In some embodiments, the density of the granular medium layer isbasically corresponding to that of the V pits, which ranges from 1×10⁷cm⁻² to 1×10⁹ cm⁻².

In some embodiments, the material of the granular medium layer can beMg_(x)N_(y), Si_(x)N_(y), Si_(x)O_(y), Ti_(x)O_(y), Zr_(x)O_(y),Hf_(x)O_(y), Ta_(x)O_(y) or any of their combinations.

According to a second aspect of the present disclosure, a fabricationmethod of a LED epitaxial structure is provided, including:

-   -   (1) providing a substrate;    -   (2) growing a first-conductive type semiconductor layer over the        substrate;    -   (3) forming a super lattice over the first-conductive type        semiconductor layer, and inserting at least one granular medium        layer during growth of the super lattice, wherein, the granular        medium layer is used for forming V pits with different widths        and depths in the super lattice;    -   (4) growing a multi-quantum well layer over the V pits and the        top surface of the super lattice;    -   (5) growing a second-conductive type semiconductor layer over        the multi-quantum well layer.

In some embodiments, grow a buffer layer over the substrate, and thematerial prefers to be InAlGaN.

In some embodiments, the first-conductive type semiconductor layerincludes an N-GaN layer, or includes a U-GaN layer and an N-GaN layer.

In some embodiments, the second-conductive type semiconductor layerincludes a P-GaN layer, or includes an electronic blocking layer and aP-GaN layer, or includes an electronic blocking layer, a P-GaN layer anda contact layer.

In some embodiments, the grain size of the granular medium layer is0.5-5 nm, and the V pits are 50-500 nm wide.

In some embodiments, the depth H of the V pits depends on the totalthickness of the super lattice T1, the total thickness of themulti-quantum well layer T2 and the position of the granular mediumlayer in the super lattice layer, and satisfies T2<H<T1+T2.

In some embodiments, density of the granular medium layer is basicallycorresponding to the V pits density, and density range of the V pits is1×10⁷ cm⁻² to 1×10⁹ cm⁻².

In some embodiments, the material of the granular medium layer can beMg_(x)N_(y), Si_(x)N_(y), Si_(x)O_(y), Ti_(x)O_(y), Zr_(x)O_(y),Hf_(x)O_(y), Ta_(x)O_(y) or any of their combinations.

In some embodiments, growing temperature for the super lattice is700-900° C.

In some embodiments, in step (3), at least one granular medium layer isinserted during super lattice growth, wherein, the super lattice is easyto form V pits over the granular medium layer from the epitaxial surfacedue to low growth temperature and poor lateral epitaxial capacity.

According to a third aspect of the present disclosure, a light-emittingsystem comprising a plurality of light-emitting diodes is provided. Eachlight-emitting diode further includes from bottom to up: a substrate, afirst-conductive type semiconductor layer, a super lattice, amulti-quantum well layer and a second-conductive type semiconductorlayer; wherein, at least one granular medium layer is embedded in thesuper lattice; wherein, the granular medium layer is used for forming Vpits with different widths and depths in the super lattice; and themulti-quantum well layer fills up the V pits and is over the top surfaceof the super lattice. The light-emitting system can be used in the fieldof, for example, lighting, display, signage, etc.

Compared with existing technologies, various embodiments of the presentdisclosure can have one or more of the technical effects: number ofmicro-particle generations, positions and densities can be adjusted byintroducing granular medium layers and controlling the number of layers,position and growth conditions during super lattice growth process, toensure match of V pits of different depths and densities. This canchange hole injection effect, effectively improve hole injectionefficiency and distribution uniformity in all quantum wells (QWs), thusimproving LED light-emitting efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and constitute a part of thisspecification, together with the embodiments, are therefore to beconsidered in all respects as illustrative and not restrictive. Inaddition, the drawings are merely illustrative, which are not drawn toscale.

In the drawings: 1: substrate; 2: buffer layer; 3: U-GaN layer; 4: N-GaNlayer; 5: super lattice; 6 (6A, 6B, 6C): granular medium layer; 7:multi-quantum well layer; 8: electronic blocking layer; 9: P-GaN layer;10: contact layer.

FIG. 1 illustrates a sectional view of the LED epitaxial structureaccording to some embodiments in the present disclosure.

FIG. 2 illustrates a top view of the LED epitaxial structure accordingto some embodiments of the present disclosure.

FIG. 3 shows a schematic diagram of hole injection positions in MQW of Vpits at different depths.

DETAILED DESCRIPTION

The present disclosure will be explained in details with reference tothe accompanying drawings. Before further description, it should beunderstood, however, that various modifications and changes may be madeto these embodiments. Therefore, the present disclosure is not limitedto the embodiments below. It should also be noted that the scope of thepresent disclosure should still be subjected to the scope defined in theclaims and the embodiments are merely for purposes of illustration,rather than restricting. Unless otherwise specified, all technical andscientific words shall have the same meanings as understood by personsskilled in the art.

Embodiment 1

With reference to FIGS. 1 and 2, an LED epitaxial structure is provided,which includes from bottom to up: a substrate 1, a buffer layer 2, afirst-conductive type semiconductor layer including a U-GaN layer 3 andan N-GaN layer 4, a super lattice 5, a multi-quantum well layer 7 and asecond-conductive type semiconductor layer comprising an electronicblocking layer 8, a P-GaN layer 9 and a contact layer 10; wherein, atleast one granular medium layer 6 is inserted in the super lattice. Thegranular medium layer 6 is used for forming V pits of different widthsand depths in the super lattice, and the multi-quantum well layer 7fills up the V pits and is over the super lattice.

Specifically, the substrate 1 in this embodiment is selected from atleast one of sapphire (Al₂O₃), SiC, GaAs, GaN, ZnO, Si, GaP, InP and Ge.In some embodiments, a plain sapphire substrate is preferred, which isnot illustrated. The sapphire substrate can also be a patterned sapphiresubstrate (PSS), but the embodiments are not limited thereto.

The buffer layer 2 is formed over the substrate 1 with InAlGaNsemiconductor material, which eliminates the lattice mismatch caused bylattice constant difference between the substrate 1 and thefirst-conductive type semiconductor layer, thus improving epitaxialgrowth quality.

The U-GaN layer 3 and the N-GaN layer 4 form a first-conductive typesemiconductor layer, which are grown over the buffer layer 2 insuccessive. The U-GaN layer 3 can eliminate the lattice mismatch causedby lattice constant difference between the substrate 1 and the N-GaNlayer 4. In addition, the U-GaN layer 3 can improve the crystallizationproperty of the semiconductor layer formed over this layer.

The super lattice 5 is formed over the first-conductive typesemiconductor layer, which is repeatedly and alternatively stacked byInGaN layers and GaN layers for about 15-25 times. Insert three granularmedium layers 6 (6A, 6B and 6C) in the super lattice 5, which are usedfor forming V pits in the super lattice. The material of the granularmedium layers is Mg_(x)N_(y), Si_(x)N_(y), Si_(x)O_(y), Ti_(x)O_(y),Zr_(x)O_(y), Hf_(x)O_(y), Ta_(x)O_(y) or any of their combinations. Inthis embodiment, Si_(x)N_(y) is preferred with grain size of 0.5-5 nm.The depth H (such as H_(6A)) of the V pits depends on the totalthickness of the super lattice T1, the total thickness of themulti-quantum well layer T2 and the position of the granular mediumlayer in the super lattice layer, and satisfies T2<H<T1+T2. The densityof the SiN granular medium layer is basically corresponding to that ofthe V pits, which ranges from 1×10⁷ cm⁻² to 1×10⁹ cm⁻².

A multi-quantum well layer 7 fills up the V pits and is over the topsurface of the super lattice 5. The multi-quantum well layer can beIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, 0≤x+y≤1) semiconductor material,which is alternatively stacked by a plurality of well layers and barrierlayers, in some embodiments, for 4-20 times.

An electronic blocking layer 8, a P-GaN layer 9 and a contact layer 10form a second-conductive type semiconductor layer, which are formed overthe multi-quantum well layer 7 in successive.

Referring to FIG. 3, QW-6A, QW-6B and QW-6C represent hole injectionconcentration of V pits of three different depths in main positions ofthe MQW. 6A is the deepest layer of V pits, wherein, when holes areinjected to the MQW through this layer of V pits, hole injection isdistributed at the bottom QW. 6B is the middle layer of V pits, wherein,when holes are injected to the MQW through this layer of V pits, holeinjection is mainly distributed in the middle QW. 6C is the shallowestlayer of V pits, wherein, when holes are injected to the MQW throughthis layer of V pits, hole injection is mainly distributed over theuppermost QW. In the present disclosure, space distribution of holes inMQW and hole injection concentration of the LED can be improved bycontrolling sizes, depths and densities of V pits of layers 6A, 6B and6C, thus improving hole injection efficiency of all QWs and lightingefficiency of LED.

Embodiment 2

Referring to FIGS. 1-2, a fabrication method of a LED epitaxialstructure is provided, which includes:

-   -   (1) providing a substrate 1, which can be at least one of        sapphire (Al₂O₃), SiC, GaAs, GaN, ZnO, Si, GaP, InP and Ge. In        some embodiments, a patterned sapphire substrate (PSS) is        preferred.    -   (2) forming a buffer layer 2 over the substrate 1. In some        embodiments, InAlGaN semiconductor material is preferred. The        epitaxial growth method can be MOCVD (metal-organic chemical        vapor deposition), CVD (chemical vapor deposition), PECVD        (plasma enhanced vapor deposition), MBE (molecular beam epitaxy)        and HVPE (hydride vapor phase epitaxy). It is preferred to be        MOCVD, but the embodiments are not limited thereto.    -   (3) growing a U-GaN layer 3 and an N-GaN layer 4 in successive        over the buffer layer 2 to form a first-conductive type        semiconductor layer.    -   (4) growing a super lattice 5 via epitaxial growth over the        first-conductive type semiconductor layer under 700-900° C.,        which is repeatedly and alternatively stacked by InGaN layers        and GaN layers for about 15-25 times. Insert 3 layers of silicon        nitride (Si_(x)N_(y)) granular medium layers 6 (6A, 6B and 6C)        in the super lattice 5. It is easy to form V pits over the        granular medium layer from the epitaxial surface due to the low        growth temperature and poor lateral epitaxial capacity of the        super lattice. In this embodiment, the grain size of the        granular medium layer prefers to be 0.5-5 nm, and the width of V        pits ranges from 50 nm to 500 nm. The depth H of the V pits        depends on the total thickness of the super lattice T1, the        total thickness of the multi-quantum well layer T2 and the        position of the granular medium layer in the super lattice        layer, and satisfies T2<H<T1+T2. The density of the granular        medium layer is basically corresponding to that of the V pits,        which ranges from 1×10⁷ cm⁻² to 1×10⁹ cm⁻². The growth sequence        of 3 granular medium layers is: 6A, 6B and 6C. The size, depth        and density of the V pits are to be optimized based on chip        design and working current. Based on theoretical calculation and        reference to experimental results, in this embodiment,        preferably, V pits depth relationship is: 6A>6B>6C; and position        depth in the super lattice relationship is: 6A>6B>6C; and        density relationship is: 6B>6C>6A.    -   (5) forming a multi-quantum well layer 7 over the V pits and the        top surface of the super lattice 5 via epitaxial growth. The        multi-quantum well layer is In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1,        0≤y≤1, 0≤x+y≤1), and is alternatively stacked by a plurality of        well layers and barrier layers, preferably, for 4-20 times.    -   (6) forming an electronic blocking layer 8, a P-GaN layer 9 and        a contact layer 10 over the multi-quantum well layer 7 via        epitaxial growth to form a second-conductive type semiconductor        layer.

Although specific embodiments have been described above in detail, thedescription is merely for purposes of illustration. It should beappreciated, therefore, that many aspects described above are notintended as required or essential elements unless explicitly statedotherwise. Various modifications of, and equivalent acts correspondingto, the disclosed aspects of the exemplary embodiments, in addition tothose described above, can be made by a person of ordinary skill in theart, having the benefit of the present disclosure, without departingfrom the spirit and scope of the disclosure defined in the followingclaims, the scope of which is to be accorded the broadest interpretationso as to encompass such modifications and equivalent structures.

The invention claimed is:
 1. A light-emitting diode, comprising: afirst-conductive type semiconductor layer; a super lattice; amulti-quantum well layer; a second-conductive type semiconductor layer;wherein, at least one medium layer having a plurality of grains thereinis embedded in the super lattice; the medium layer is used for forming Vpits with different widths and depths in the super lattice; themulti-quantum well layer fills up the V pits and is over a top surfaceof the super lattice; and a density of the plurality of grains in themedium layer is approximately same as that of the V pits.
 2. Thelight-emitting diode of claim 1, wherein, sizes of the plurality ofgrains in the medium layer are 0.5-5 nm, and the V pits are 50-500 nmwide.
 3. The light-emitting diode of claim 1, wherein, the depth H ofthe V pits depends on a total thickness of the super lattice T1, a totalthickness of the multi-quantum well layer T2 and a position of themedium layer in the super lattice layer, and satisfies T2<H<T1+T2. 4.The light-emitting diode of claim 1, wherein, the density of theplurality of grains in the medium layer ranges from 1×10⁷ cm⁻² to 1×10⁹cm⁻².
 5. The light-emitting diode of claim 1, wherein, the medium layercomprises at least one of Mg_(x)N_(y), Si_(x)N_(y), Si_(x)O_(y),Ti_(x)O_(y), Zr_(x)O_(y), Hf_(x)O_(y), or Ta_(x)O_(y).
 6. Thelight-emitting diode of claim 1, wherein, three granular medium layersare inserted during growth of the super lattice.
 7. A method offabricating the light-emitting diode according to claim 1, the methodcomprising: (1) providing a substrate; (2) growing a first-conductivetype semiconductor layer over the substrate; (3) forming a super latticeover the first-conductive type semiconductor layer, and inserting atleast one medium layer having a plurality of grains therein duringgrowth of the super lattice, wherein, the medium layer is used forforming V pits with different widths and depths in the super lattice;(4) growing a multi-quantum well layer over the V pits and a top surfaceof the super lattice; (5) growing a second-conductive type semiconductorlayer over the multi-quantum well layer.
 8. The fabrication method ofclaim 7, wherein: sizes of the plurality of grains in the medium layerare 0.5-5 nm, and the V pits are 50-500 nm wide.
 9. The fabricationmethod of claim 7, wherein, the depth H of the V pits depends on a totalthickness of the super lattice T1, a total thickness of themulti-quantum well layer T2 and a position of the granular medium layerin the super lattice layer, and satisfies T2<H<T1+T2.
 10. Thefabrication method of claim 7, wherein, the density of the plurality ofgrains in the medium layer ranges from 1×10⁷ cm⁻² to 1×10⁹ cm⁻².
 11. Thefabrication method of claim 7, wherein, the medium layer comprises atleast one of Mg_(x)N_(y), Si_(x)N_(y), Si_(x)O_(y), Ti_(x)O_(y),Zr_(x)O_(y), Hf_(x)O_(y), or Ta_(x)O_(y).
 12. The fabrication method ofclaim 7, wherein, a growth temperature for the super lattice is 700-900°C.
 13. The fabrication method of claim 7, wherein, in step (3), at leastone medium layer is inserted during growth of the super lattice; therebyfacilitating the super lattice to form the V pits at the medium layerfrom an epitaxial surface due to low growth temperature and poor lateralepitaxial capacity.
 14. A light-emitting system comprising a pluralityof light-emitting diodes, wherein each light-emitting diode comprises: afirst-conductive type semiconductor layer; a super lattice; amulti-quantum well layer; a second-conductive type semiconductor layer;wherein, at least one medium layer having a plurality of grains thereinis embedded in the super lattice; the medium layer is used for forming Vpits with different widths and depths in the super lattice; themulti-quantum well layer fills up the V pits and is over a top surfaceof the super lattice; and a density of the plurality of grains in themedium layer is approximately same as that of the V pits.
 15. Thelight-emitting system of claim 14, wherein, sizes of the plurality ofgrains in the medium layer are 0.5-5 nm, and the V pits are 50-500 nmwide.
 16. The light-emitting system of claim 14, wherein, the depth H ofthe V pits depends on a total thickness of the super lattice T1, a totalthickness of the multi-quantum well layer T2 and a position of thegranular medium layer in the super lattice layer, and satisfiesT2<H<T1+T2.
 17. The light-emitting system of claim 14, wherein, thedensity of the plurality of grains in the medium layer ranges from1×10⁷cm⁻² to 1×10⁹cm⁻².
 18. The light-emitting system of claim 14,wherein, the medium layer comprises at least one of Mg_(x)N_(y),Si_(x)N_(y), Si_(x)O_(y), Ti_(x)O_(y), Zr_(x)O_(y), Hf_(x)O_(y), orTa_(x)O_(y).
 19. The light-emitting system of claim 14, wherein, threemedium layers are inserted during growth of the super lattice.
 20. Thelight-emitting system of claim 14, wherein, a growth temperature for thesuper lattice is 700-900° C.